1. Field of the Invention
The present invention relates to an optical disc reproducing apparatus and method, and more particularly to an optical disc reproducing apparatus for displaying text such as caption data, program menu data, reproduction information, etc., on a display screen using a single character generating device.
2. Description of Related Art
A greater demand exits in the industry for techniques which allow large amounts of information to be densely recorded upon recording media. Development has focused on recording media such as compact discs, digital video discs (DVD), etc., to meet this need.
A DVD reproducing apparatus has been designed to reproduce data recorded on a DVD (diameter: 12 cm, thickness: 1.2 mm) for about 135 minutes, and to provide better image and sound quality than a laser disc. Accordingly, a DVD device is one of the noticeable multi-media devices in audio/video and computer applications. DVDs are widely used in image processing applications due to their large storage capacity. One of the DVD system formats has system specifications as follows:
1. Maximum 9 camera angles reproducible;
2. Maximum 8 channels for audio and 32 languages as a caption;
3. Storage of a plurality of user selectable programs, selectable via a menu screen; and
4. Provision of parental lock function which can prevent children from watching adult programs.
According to the above system specification, the structure of the data stream used in DVDs is shown in FIG. 1. This data stream includes a video stream, an audio stream, and a sub-picture stream. Although not shown, the data stream also includes control data which is used during reproduction to control the reproducing operation. The video stream includes video or image data such as for a moving image, the audio stream includes audio data such as voice and/or sound data, and the sub-picture stream includes caption data to be displayed on a display screen during reproduction. As also shown in FIG. 1, the audio data includes multiple channels.
A conventional optical disc reproducing apparatus using the above-described data stream structure will be described with reference to FIG. 2. As shown in FIG. 2, the optical disc reproducing apparatus for reproducing data from an optical disc 1 includes a motor 11 for rotating the optical disc 1; an optical pick-up 3 for reading the data recorded on the optical disc 1; a servo circuit 13 for generating drive signals to control the operation of the motor 11 and the optical pick-up 3; and microprocessor 15 for controlling the operation of the servo circuit 13, a signal processing circuit 5, an error correction circuit 7, a navigator 17, and an on screen display (OSD) unit 31 based on key input from a user.
In accordance with the instructions received from the microprocessor 15, the signal processing circuit 5 amplifies the reproduced signal output from the optical pick-up 3, and performs phase compensation thereon. The microprocessor 15 also obtains management and sub-management data from the reproduced signal processed by the signal processing circuit 5. The management data includes table of contents (TOC) data such as recorded in the lead-in area of the optical disk 1. The sub-management data includes characteristic information for the data recorded on the optical disk such as recorded in the headers of logically grouped data. With respect to a DVD, the characteristic information could indicate which camera angle from the plurality of camera angles the data in the following logical group represents, or could indicate that the data in the following logical group is English language caption data.
The error correction circuit 7 corrects, under the control of the microprocessor 15, errors in the bit stream of the reproduced signal output by the signal processing circuit 5. A variable transfer rate (VBR) buffer 9 temporarily stores the error corrected reproduced signal. The navigator 17 controls the transfer of data from the VBR buffer 9 to a data decoding section 30 in part based on control signals from the microprocessor 15 and in part based on the control data extracted from the bit stream of the reproduction signal output from the VBR buffer 9.
The data decoding section 30 includes a video decoding part 21, a graphics circuit 24, and an audio decoding part 27 operating under the control of the navigator 17. The graphics circuit 24 receives the output of the VBR buffer 9 via the video decoding part 21, and the audio decoding part 27 receives the output of the VBR buffer 9 via the graphics circuit 24 and the video decoding part 21.
A mixer 43 mixes the output of the video decoding part 21 and the graphics circuit 24 to produce a digital video signal. A first digital/analog converter 23 digital-to-analog converts the digital video signal, while a second digital/analog converter 29 digital-to-analog converts the output of the audio decoding part 27.
The OSD unit 31, under the control of the microprocessor 15, adds character data representing reproduction information to the analog video signal output by the first digital/analog converter 23 to produce an output video signal.
Next, the operation of the conventional optical disc reproducing apparatus will be described. After mounting the optical disc 1 on a turntable (not shown), the user selects a specific system function and options associated therewith using a plurality of input keys (not shown). For instance, after selecting a basic reproduction operation, the user can select the reproduction characteristics. The reproduction characteristics include, for example, the camera angle to be reproduced, that a caption should be displayed, and the language of the caption. If the user does not elect to select the reproduction characteristics, then the basic reproduction operation will proceed according to predetermined default reproduction characteristics.
When the user selects a reproduction operation, the microprocessor 15 controls the servo circuit 13 to drive the motor 11 and the optical pick-up 3. According to the drive signals from the servo circuit 13, the optical pick-up 3 reproduces data recorded on the optical disc 1. The reproduced data is converted into an electrical signal and output to the signal processing circuit 5. The signal processing circuit 5 performs a predetermined signal processing operation such as noise amplification, phase compensation, etc., on the electrical signal (i.e., the reproduced signal) in accordance with the instructions received from the microprocessor 15, and the microprocessor 15 extracts the management and sub-management data from the processed reproduced signal.
The processed reproduced signal is output to the error correction circuit 7. The error correction circuit 7 corrects errors generated in the reproduced signal in a predetermined manner as instructed by the microprocessor 15. The error corrected reproduced signal is then output to and temporarily stored by the VBR buffer 9. Based on the reproduction characteristics and the management and sub-management data, the navigator 17 controls the transfer of data from the VBR buffer 9 to the data decoding section 30. Because frames of video data are compressed to different sizes according to the characteristics of the images in the frame, the quantity of data input by the VBR buffer 9 varies. In order to store variably transferred data, yet output a continuous and seamless stream of data, the VBR buffer 9, under the control of the navigator 17, is used.
As discussed above with respect to FIG. 1, the data output from the VBR buffer 9 includes system related control data, video data, sub-picture data, (e.g, caption and menu selection data), and audio data. The navigator 17 extracts the control data, and controls the operation of the data decoding section based in part thereon.
The data output from the VBR buffer 9 is received by the video decoding part 21 of the data decoding section 30. The video decoding part 21 extracts, decompresses, and decodes the video data in the bit stream output from the VBR buffer 9 under the control of the navigator 17. The video decoding part 21 then outputs the processed video data to the mixer 43. The video decoding part 21 also passes the bit stream from the VBR buffer 9 to the graphics circuit 24.
The graphics circuit 24 extracts and decodes the sub-picture data in the bit stream from the VBR buffer 9, and outputs the decoded sub-picture data to the mixer 43. FIG. 3 is a detailed block diagram of the conventional graphics circuit 24. As shown in FIG. 3, the graphics circuit 24 includes a data extracting part 33 for extracting the sub-picture data in the bit stream output from the VBR buffer 9. A timing circuit 35 also receives the bit stream output by the VBR buffer 9, and detects a sync signal from the video data included in the bit stream. Based on the detected sync signal, the timing circuit 25 generates a clock signal.
The graphics circuit 24 further includes a decoder 37 and a first character memory 39. The decoder 37 receives the sub-picture data output by the data extracting part 33, and decodes the sub-picture data. The decoded sub-picture data is then stored in the first character memory 39. In accordance with the clock signal output by the timing circuit 35, the first character memory 39 outputs the decoded sub-picture data for display at a predetermined position on the display screen. The decoded sub-picture data output by the first character memory 39 is amplified by a level controller 41, and output to the mixer 43. The mixer 43 mixes the processed video data output by the video decoding part 21 with the amplified decoded sub-picture data to produce a digital video signal.
As shown in FIG. 2, the first digital/analog converter 23 converts the digital video signal output by the mixer 43 into an analog video signal. The OSD unit 31 receives the analog video signal, and mixes a character signal with the analog video signal under the control of the microprocessor 15.
FIG. 4 is a detailed block diagram of the conventional OSD unit 31. As shown in FIG. 4, a timing circuit 45 receives the analog video signal, detects a sync signal in the video signal portion of the analog video signal, and generates a clock signal according to the detected sync signal and instructions from a controller 47. The controller 47 receives clock data and character control instructions from the microprocessor 15. The clock data indicates when the clock signal should be output from the timing circuit 45. In accordance with the clock data, the controller 47 outputs instructions to the timing circuit 45. The controller 47 also converts the character control instructions into memory addresses, and outputs the memory addresses to a second character memory 49. The second character memory 49 stores the text of, for example, reproduction information such as time information and operation information (e.g., play, rewind, fast forward, camera angle, etc.). The character control instructions specify the reproduction information the second character memory 49 is to output.
Based on the clock signal, the second character memory 49 outputs the text or character data addressed by the memory addresses from the controller 47 to a level controller 51. Accordingly, the clock signal (i.e., the clock data from the microprocessor 15) specifies the position on the display where this character data will appear. The level controller 51 amplifies the character data output from the second character memory 49, and converts the amplified data into an analog character signal. This analog character signal is then mixed by a mixer 53 with the analog video signal output from the mixer 43 to produce an output video signal.
As shown in FIG. 3, the bit stream output by the VBR buffer 9 is transferred from the video decoding part 21 and the graphics circuit 24 to the audio decoding part 27. Based on instructions from the navigator 17, the audio decoding part 27 extracts and decodes the audio data in this bit stream. The second analog converter 29 converts the audio data into an output audio signal.
As discussed above, both the graphics circuit 24 and the OSD unit 31 output data, which is mixed with video data, to display text on a display screen. As such, elements forming the graphics circuit 24 are duplicated in the OSD unit 31. As a result, the conventional optical disc reproducing apparatus is large, complex, and costly.
Furthermore, the video data in the bit stream output by the VBR buffer 9 undergoes several processes (e.g., extraction, decoding, conversion, mixing). Each signal processing procedure degrades the signal-to-noise ratio of the resulting output video signal such that image quality is deteriorated and the display of characters can become distorted.
One object of the present invention is to provide an optical disc reproducing apparatus and method which overcome the problems and disadvantages discussed above.
Another object of the present invention is to provide an optical disc reproducing apparatus which is smaller, less complex, and less costly than conventional optical reproducing apparatuses.
A further object of the present invention is to provide an optical disc reproducing apparatus which uses a single character generating device to display sub-picture data and reproduction information.
Another object of the present invention is to provide an optical disc reproducing apparatus which digitally processes sub-picture data and reproduction information to be displayed on a display screen.
These and other objectives are achieved by providing an optical disc reproducing apparatus, comprising: an optical pick-up for reproducing a digital signal from an optical disc, said reproduced digital signal including at least video data and sub-picture data; and processing means for storing a plurality of text portions, for receiving character control instructions, for receiving said reproduced digital signal, for generating first character data representing at least one of said plurality of text portions based on said character control instructions, for generating second character data based on said sub-picture data in said reproduced digital signal, and for generating a digital video signal based on said first and second character data and said video data in said reproduced digital signal.
These and other objectives are further achieved by providing an optical disc reproducing apparatus, comprising: an optical pick-up for reproducing a signal from an optical disc, said reproduced signal including at least video data and sub-picture data; a video decoder decoding said video data in said reproduced signal; and a graphics circuit storing a plurality of text portions, receiving character control instructions, receiving said reproduced signal, generating first character data representing at least one of said plurality of text portions based on said character control instructions, and generating second character data based on said sub-picture data in said reproduced signal.
These and other objectives are also achieved by providing an optical disc reproducing method, comprising: reproducing a digital signal from an optical disc, said reproduced digital signal including at least video data and sub-picture data; storing a plurality of text portions; receiving character control instructions; generating first and second character data based on said character control instructions and said sub-picture data in said reproduced digital video signal, said first character data representing at least one of said plurality of text portions; and generating a digital video signal based on said first and second character data and said video data.
These and other objectives are additionally achieved by providing an optical disc reproducing apparatus, comprising: an optical pick-up for reproducing a signal from an optical disc, said reproduced signal including at least video data and sub-picture data; and processing means for storing a plurality of text portions in a single memory, for receiving character control instructions, for receiving said reproduced digital signal, for generating, using said single memory, first character data representing at least one of said plurality of text portions based on said character control instructions, and for generating, using said single memory, second character data based on said sub-picture data in said reproduced signal.
Other objects, features, and characteristics of the present invention; methods, operation, and functions of the related elements of the structure; combination of parts; and economies of manufacture will become apparent from the following detailed description of the preferred embodiments and accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures.